This invention relates to a process for manufacturing reinforced sealing gaskets, by depositing elastomeric polymers and the like, while in the fluid state, and subsequently curing them. The invention also relates to the product obtained by such process.
Planar gaskets made by depositing and then curing a thread of a fluid elastomer or other polymer onto a non-adhesive support and then moving the cured thread for use as a gasket have been known for some time. Moreover, in the copending U.S. patent application Ser. No. 695830 for "Process for making sealing gaskets, and gasket so obtained", claiming priority of Italian Pat. Appln. No. 67974-A/84, the Applicant has now proposed a technique of deposition of a fluid material by which non-planar gaskets can be economically obtained.
A technique of assembly has become recently widespread, particularly in the automobile industry, whereby, for sealing statically coupled surfaces, the conventional gasket is replaced with a thread of an elastomer which is directly deposited, while in the fluid state, onto the surface of the part, the elastomer being subsequently cured so that it becomes bonded to the surface. Deposition is made from a nozzle that is displaced by numerically controlled manipulators capable of moving along two or three coordinates.
The above technique dispenses with the fixed costs of the molds or dies required for the manufacture of conventional gaskets made by punching or injection-molding, while the quality is kept at a level equal or superior to the quality obtainable with a conventional gasket. In particular, such method of assembly is especially advantageous with non-planar layouts, because it then replaces a gasket that otherwise would have to be made by injection-molding, and therefore inherently expensive.
However, such method of direct deposition on the part during assembly is not free from practical drawbacks. If the deposition station breaks down, it is not always possible to substitute readymade gaskets, as these may not yet be available commercially. Even when nozzle-deposited spare gaskets are available, these are soft and supple, and therefore not adapted to be manipulated by robots. If the gasket has a planar outline, it may be possible to use punched reinforced gaskets, which are stiff and relatively cheap. However, in the case of non-planar gaskets, where direct deposition affords its best usefulness, manufactures, in order to avoid the shutdown of the entire assembly line, have to provide expensive emergency equipment, which defeats to a large extent the saving inherent in direct deposition.
Another drawback of nozzle-deposited gaskets is that, because of their high compliance, they will run out and even be disintegrated if subjected to strong pressure. Their degree of compliance can be adjusted only to a limited extent, because of the inherent softness of the materials used, such as silicones and polyurethanes. As a consequence of this shortcoming, nozzle-deposited gaskets have been kept away from many applications where their low cost and easy adaptability would otherwise make them attractive.